Wireless communications has been widely applied globally, which greatly facilitates communication between people. The wireless communications can provide a variety of services, including voice calls, webpage downloads, and the like. A typical wireless communications system or network, for example, a Long Term Evolution (LTE) system provides, in a cellular cell, a radio link for multiple user equipment (UE) using a base station, to implement wireless communication. For the wireless connection, a shared wireless spectrum is generally used.
With the development of the Internet, new services are constantly emerging. However, performance of many services in a wireless network still cannot meet people's needs. Mobile streaming media services are classified into play online and play after download, where play online supports both play on live and play on demand. Compared with play after download, play online can greatly reduce a start-up delay, avoiding a drawback that a user can view a file only after the entire file is completely downloaded from a server. In a process of playing mobile streaming media online, an ideal situation is that a transmission bandwidth is maintained to be slightly larger than an encoding bandwidth of media content being transmitted. However, an encoding rate of the media content may change, for example, variable bit rate (VBR) video or audio; and a radio resource required by each user may not always be guaranteed due to a problem of wireless spectrum sharing in a wireless network. In addition, a wireless channel for communication between a user and a base station has an attenuating characteristic, which results in fluctuation of a wireless communications rate, thereby further affecting stability of streaming media transmission, causing a stuttering or mosaic phenomenon in a process of playing on a receiving terminal of the user, and affecting the user's experience in media playing. A same problem also occurs in a wireless video call.
Dynamic adaptive streaming over Hypertext Transfer Protocol (DASH) is used on the Internet to provide good experience in play on live and play on demand of streaming media. DASH is used to transmit high-speed video and audio data over the Hypertext Transfer Protocol (HTTP). HTTP has been well supported on the Internet and can easily penetrate a firewall, which reduces implementation costs of DASH. That a client adaptively requests, based on the HTTP protocol, content from a server also greatly reduces pressure on the server, so that the server does not need to store statuses of a large number of users, which can effectively increase a quantity of users served by the server. A typical application of DASH is shown in FIG. 1. A media presentation description (MPD) file and a media segment file are stored on a server. The MPD file includes related information of the media segment file, such as a time length, a file size, a play start time, a file storage website, a media type, and a resolution that are of the media segment file. The media segment file stores actual play data of streaming media, where the actual play data of streaming media may be stored in one or more files. Generally, a manner of using multiple files is used, where one segment, for example, media content of 2 seconds, is stored in one file. To adapt to different network bandwidth conditions, same media content is stored in different files according to different encoding rates. For example, for transmission rates of 5 megabits per second (Mbps), 2 Mbps, and 500 kilobits per second (Kbps), three different files of the media content of which average encoding rates are 4.8 Mbps, 1.7 Mbps, and 490 Kbps respectively may be prepared and stored on the server. A media file can be played online smoothly only when a transmission rate is higher than an encoding rate of the media file.
When a user expects to accept a DASH service, a terminal needs to first acquire the MPD file from the server, where the file may be acquired in multiple manners, for example, by means of broadcasting or by performing direct acquisition from the server using an HTTP request. After acquiring the MPD file, the terminal knows the information about the media segment file on the server, such as the type, a storage location, a length of each segment, the file size, and the like of the media segment file. The terminal can also measure a transmission bandwidth of an entire network from the server to the terminal, and determine a transmission rate of a media segment file for which the terminal needs to apply to the server. For example, when the terminal measures that the transmission bandwidth of the network is greater than 5 Mbps, the terminal may apply to the server for a media segment that is for a transmission rate of 5 Mbps (that is, a media file of which an average encoding rate is less than and closer to 5 Mbps); and if the transmission bandwidth of the network is only 3 Mbps, the terminal applies to the server for only a media segment file that is for a transmission rate of 2 Mbps, and does not apply for a file that is for a transmission rate of 5 Mbps, so as to avoid network transmission congestion and influence on the user's experience.
When the foregoing method is applied in a wired environment, pressure of adaptive processing may be placed on the terminal, thereby reducing a burden on the server and increasing a quantity of users that is served by the server at the same time. However, when the method is applied in a wireless environment, or when at least a part of an entire transmission process involves wireless transmission, due to the existence of the foregoing wireless problem, a transmission rate measured by the terminal cannot be guaranteed in a wireless network, therefore performance of the terminal is significantly deteriorated.
Currently, there are some solutions that implement online playing of mobile streaming media in a wireless environment. An existing method for configuring a minimum rate on UE (user equipment, user equipment) is shown in FIG. 2. The UE selects a guaranteed bit rate (GBR) according to an option provided by a network, and sends the GBR to the network using a request message for confirmation. After the confirmation, the UE can perform communication according to an agreed GBR. However, in this solution, the GBR is selected by means of user input, which corresponds to the second step in FIG. 2 of selecting a specific bit rate. Apart from this method, this solution does not disclose another method for selecting a rate to ensure experience of a mobile streaming media service. Considering a change of an objective condition of a wireless environment, for example, channel fading, and a change of a size of a media file, for example a VBR video, that is, a change of a media encoding compression ratio, it is obvious that, by means of user selection, an adaptive adjustment of a transmission rate in real time cannot be supported.
According to an existing streaming media transmission method, a receiving side acquires at least a maximum bit rate or a maximum service data unit size for transmission, thereby achieving an objective of reserving network resources. In the method, when a user selects media to view, wireless user equipment sends a request to a wireless network, and the request is sent to a streaming media server. The streaming media server checks content of the request, and acquires related information, where the related information should include at least a maximum bit rate. The information is then transmitted to the wireless network and the wireless user equipment from the streaming media server. The wireless user equipment sends a request including at least the maximum bit rate to the wireless network, and the wireless network selects a bearer service. A transmission parameter selected by the wireless network may be lower than a requested rate. A selection result of the wireless network is transmitted back to the wireless user equipment, and a connection is established for communication. This solution is different from a DASH method. In this method, the server needs to acquire information about the maximum bit rate and transmit the information back to the wireless network and the wireless user equipment. Compared with a manner, in the DASH method, of determining a rate completely by a terminal and directly requesting related content, this method increases a burden of the server. Secondly, a manner of reserving resources using a maximum bit rate is a conventional circuit switched (CS) communication method. This method causes a waste of resources because reserved resources cannot be allocated to other users for use. As described above, in wireless communications, valuable wireless spectrum resources serve multiple users at the same time in a shared manner. For a case in which media encoding compression ratios are different, especially when a VBR video service is provided, this manner of reserving resources according to a maximum bit rate greatly wastes wireless spectrum resources. Finally, in the DASH method, an MPD file is transmitted to wireless user equipment for analysis, and an analysis result does not need to be sent to a wireless network. Therefore, the wireless network does not know a real need of a user for a media service, and a bearer service selected by the wireless network may meet an experience need of the user. However, in the foregoing method, the wireless user equipment does not implement a corresponding remedial measure for this situation.